Browsing by Author "Pollack, S.E."

Now showing 1 - 4 of 4
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    Collective excitation of a Bose-Einstein condensate by modulation of the atomic scattering length
    (American Physical Society, 2010) Pollack, S.E.; Dries, D.; Hulet, R.G.; Magalhães, K.M.F.; Henn, E.A.L.; Ramos, E.R.F.; Caracanhas, M.A.; Bagnato, V.S.; Rice Quantum Institute
    We excite the lowest-lying quadrupole mode of a Bose-Einstein condensate by modulating the atomic scattering length via a Feshbach resonance. Excitation occurs at various modulation frequencies, and resonances located at the natural quadrupole frequency of the condensate and at the first harmonic are observed. We also investigate the amplitude of the excited mode as a function of modulation depth. Numerical simulations based on a variational calculation agree with our experimental results and provide insight into the observed behavior.
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    Dissipative transport of a Bose-Einstein condensate
    (American Physical Society, 2010) Dries, D.; Pollack, S.E.; Hitchcock, J.M.; Hulet, R.G.; Rice Quantum Institute
    We investigate the effects of impurities, either correlated disorder or a single Gaussian defect, on the collective dipole motion of a Bose-Einstein condensate of Li7 in an optical trap. We find that this motion is damped at a rate dependent on the impurity strength, condensate center-of-mass velocity, and interatomic interactions. Damping in the Thomas-Fermi regime depends universally on the disordered potential strength scaled to the condensate chemical potential and the condensate velocity scaled to the speed of sound. The damping rate is comparatively small in the weakly interacting regime, and, in this case, is accompanied by strong condensate fragmentation. In situ and time-of-flight images of the atomic cloud provide evidence that this fragmentation is driven by dark soliton formation.
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    Extreme Tunability of Interactions in a Li7 Bose-Einstein Condensate
    (American Physical Society, 2009) Pollack, S.E.; Dries, D.; Junker, M.; Chen, Y.P.; Corcovilos, T.A.; Hulet, R.G.; Rice Quantum Institute
    We use a Feshbach resonance to tune the scattering length a of a Bose-Einstein condensate of Li7 in the |F=1,mF=1⟩ state. Using the spatial extent of the trapped condensate, we extract a over a range spanning 7 decades from small attractive interactions to extremely strong repulsive interactions. The shallow zero crossing in the wing of the Feshbach resonance enables the determination of a as small as 0.01 Bohr radii. Evidence of the weak anisotropic magnetic dipole interaction is obtained by comparison with different trap geometries for small a.
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    Finite-range corrections near a Feshbach resonance and their role in the Efimov effect
    (American Physical Society, 2013) Dyke, P.; Pollack, S.E.; Hulet, R.G.; Rice Quantum Institute
    We have measured the binding energy of 7Li Feshbach molecules deep into the nonuniversal regime by associating atoms in a Bose-Einstein condensate with a modulated magnetic field. We extract the scattering length from these measurements, correcting for nonuniversal short-range effects using the field-dependent effective range. With this more precise determination of the Feshbach resonance parameters we reanalyze our previous data on the location of atom loss features produced by the Efimov effect [Pollack et al., Science 326, 1683 (2009)]. We find the measured locations of the three- and four-body Efimov features to be consistent with universal theory at the 20%-30% level.